Run prettier across the repo, exclude the lockfile from it

Prettier had never been run in --check mode here before, so this had
drifted across most files (markdown tables, long option() chains,
line wrapping). Purely formatting, no logic changes - needed so a CI
format:check gate can actually pass. Adds .prettierignore for
pnpm-lock.yaml specifically: prettier's YAML formatter rewrites every
quoted key (single -> double quotes) producing an ~8700-line diff of
pure noise on a file pnpm itself owns the formatting of.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/API.md

@@ -77,7 +77,7 @@ code). `404` if not found.
 
 ### `POST /api/runs/:runId/cancel`
 
-`202 {"status": "cancelling"}`. `409` if the run already finished, or if it isn't tracked by *this*
+`202 {"status": "cancelling"}`. `409` if the run already finished, or if it isn't tracked by _this_
 server process (e.g. after a restart — see "orphaned runs" in `docs/ARCHITECTURE.md`).
 
 ### `GET /api/runs/:runId/logs`